IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specification for implementing wireless local area network (WLAN) communication in the WI-FI (2.4, 3.6, 5, and 60 GHz) frequency bands. The 802.11 family consists of a series of half-duplex over-the-air modulation techniques that use the same basic protocol. The standards and amendments provide the basis for wireless network products using the WI-FI frequency bands. For example, IEEE 802.11ac is a wireless networking standard in the IEEE 802.11 family providing high-throughput WLANs on the 5 GHz band. Significant wider channel bandwidths (20 MHz, 40 MHz, 80 MHz, and 160 MHz) were proposed in the IEEE 802.11ac standard. The High Efficiency WLAN study group (HEW SG) is a study group within IEEE 802.11 working group that will consider the improvement of spectrum efficiency to enhance the system throughput in high-density scenarios of wireless devices. Because of HEW SG, TGax (an IEEE task group) was formed and tasked to work on IEEE 802.11ax standard that will become a successor to IEEE 802.11ac. Recently, WLAN has seen exponential growth across organizations in many industries.
In IEEE 802.11ac, a transmitter of a BSS (basic service set) of certain bandwidth is allowed to transmit radio signals onto the shared wireless medium depending on clear channel assessment (CCA) sensing and a deferral or backoff procedure for channel access contention. An enhanced distributed channel access (EDCA) protocol is used in IEEE 802.11ac as a channel contention procedure for wireless devices to gain access to the shared wireless medium, e.g., to obtain a transmitting opportunity (TXOP) for transmitting radio signals onto the shared wireless medium.
With EDCA, high-priority traffic has a higher chance of being sent than low-priority traffic. A station with high priority traffic waits a little less before it sends its packet than a station with low priority traffic. The levels of priority in EDCA are called access categories (ACs). For example, ACs map directly from Ethernet-level class of service (CoS) priority levels indicated via a priority code point (PCP) associated with a traffic type, e.g. a traffic ID. The EDCA parameters for each AC are set differently according to the traffic type. The traffic in different ACs cannot be sent in the same packet for contention fairness consideration. In legacy WLAN, different AC traffic cannot be transmitted in an A-MPDU for contention fairness consideration.
Orthogonal frequency division multiple access (OFDMA) technology is developed in the cellular network enabling multiple users sharing the same wideband at the same time. How to adapt the OFDMA technology to the WLAN to enable multiple users sharing the same wideband remains a question. In OFDMA wireless systems, contention-based uplink transmission is commonly used for multiple user equipments (UEs) to transmit uplink data to a serving base station via a shared uplink channel. For example, an STA may request access and acquire ownership of an uplink channel to initiate transmission. Therefore, in WLAN, contention-based random access can also be used for uplink OFDMA operation.
In OFDMA, the air time of scheduled DL/UL OFDMA resource unit (RU) is limited by the STA that requires the longest air time. The condition of fairness consideration is totally different as compared to legacy WLAN. Other STAs may have long idle time. It is desirable to utilize the idle time efficiently. Furthermore, for downlink or uplink (DL/UL) OFDMA, to align the timing for all the multi-user transmission, idle time may be introduced for some DL/UL resource units (RUs) and padding may be required. Further improvements on utilization of resource unit (RUs) is also desired.